Re: [PATCH v2 2/2] perf annotation: Switch lock from a mutex to a sharded_mutex

[Namhyung Kim]

On Wed, Jun 14, 2023 at 9:07 PM Ian Rogers <irogers@xxxxxxxxxx> wrote:
>
> Remove the "struct mutex lock" variable from annotation that is
> allocated per symbol. This removes in the region of 40 bytes per
> symbol allocation. Use a sharded mutex where the number of shards is
> set to the number of CPUs. Assuming good hashing of the annotation
> (done based on the pointer), this means in order to contend there
> needs to be more threads than CPUs, which is not currently true in any
> perf command. Were contention an issue it is straightforward to
> increase the number of shards in the mutex.
>
> On my Debian/glibc based machine, this reduces the size of struct
> annotation from 136 bytes to 96 bytes, or nearly 30%.
>
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung

> ---
>  tools/perf/builtin-top.c          | 14 +++----
>  tools/perf/ui/browsers/annotate.c | 10 ++---
>  tools/perf/util/annotate.c        | 66 ++++++++++++++++++++++++++-----
>  tools/perf/util/annotate.h        | 11 ++++--
>  4 files changed, 77 insertions(+), 24 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index c363c04e16df..1baa2acb3ced 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -137,10 +137,10 @@ static int perf_top__parse_source(struct perf_top *top, struct hist_entry *he)
>         }
>
>         notes = symbol__annotation(sym);
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>
>         if (!symbol__hists(sym, top->evlist->core.nr_entries)) {
> -               mutex_unlock(&notes->lock);
> +               annotation__unlock(notes);
>                 pr_err("Not enough memory for annotating '%s' symbol!\n",
>                        sym->name);
>                 sleep(1);
> @@ -156,7 +156,7 @@ static int perf_top__parse_source(struct perf_top *top, struct hist_entry *he)
>                 pr_err("Couldn't annotate %s: %s\n", sym->name, msg);
>         }
>
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>         return err;
>  }
>
> @@ -211,12 +211,12 @@ static void perf_top__record_precise_ip(struct perf_top *top,
>
>         notes = symbol__annotation(sym);
>
> -       if (!mutex_trylock(&notes->lock))
> +       if (!annotation__trylock(notes))
>                 return;
>
>         err = hist_entry__inc_addr_samples(he, sample, evsel, ip);
>
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>
>         if (unlikely(err)) {
>                 /*
> @@ -253,7 +253,7 @@ static void perf_top__show_details(struct perf_top *top)
>         symbol = he->ms.sym;
>         notes = symbol__annotation(symbol);
>
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>
>         symbol__calc_percent(symbol, evsel);
>
> @@ -274,7 +274,7 @@ static void perf_top__show_details(struct perf_top *top)
>         if (more != 0)
>                 printf("%d lines not displayed, maybe increase display entries [e]\n", more);
>  out_unlock:
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>  }
>
>  static void perf_top__resort_hists(struct perf_top *t)
> diff --git a/tools/perf/ui/browsers/annotate.c b/tools/perf/ui/browsers/annotate.c
> index 70bad42b807b..ccdb2cd11fbf 100644
> --- a/tools/perf/ui/browsers/annotate.c
> +++ b/tools/perf/ui/browsers/annotate.c
> @@ -314,7 +314,7 @@ static void annotate_browser__calc_percent(struct annotate_browser *browser,
>
>         browser->entries = RB_ROOT;
>
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>
>         symbol__calc_percent(sym, evsel);
>
> @@ -343,7 +343,7 @@ static void annotate_browser__calc_percent(struct annotate_browser *browser,
>                 }
>                 disasm_rb_tree__insert(browser, &pos->al);
>         }
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>
>         browser->curr_hot = rb_last(&browser->entries);
>  }
> @@ -470,10 +470,10 @@ static bool annotate_browser__callq(struct annotate_browser *browser,
>         }
>
>         notes = symbol__annotation(dl->ops.target.sym);
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>
>         if (!symbol__hists(dl->ops.target.sym, evsel->evlist->core.nr_entries)) {
> -               mutex_unlock(&notes->lock);
> +               annotation__unlock(notes);
>                 ui__warning("Not enough memory for annotating '%s' symbol!\n",
>                             dl->ops.target.sym->name);
>                 return true;
> @@ -482,7 +482,7 @@ static bool annotate_browser__callq(struct annotate_browser *browser,
>         target_ms.maps = ms->maps;
>         target_ms.map = ms->map;
>         target_ms.sym = dl->ops.target.sym;
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>         symbol__tui_annotate(&target_ms, evsel, hbt, browser->opts);
>         sym_title(ms->sym, ms->map, title, sizeof(title), browser->opts->percent_type);
>         ui_browser__show_title(&browser->b, title);
> diff --git a/tools/perf/util/annotate.c b/tools/perf/util/annotate.c
> index cdd1924a4418..7cae73bb7353 100644
> --- a/tools/perf/util/annotate.c
> +++ b/tools/perf/util/annotate.c
> @@ -32,6 +32,7 @@
>  #include "block-range.h"
>  #include "string2.h"
>  #include "util/event.h"
> +#include "util/sharded_mutex.h"
>  #include "arch/common.h"
>  #include "namespaces.h"
>  #include <regex.h>
> @@ -856,7 +857,7 @@ void symbol__annotate_zero_histograms(struct symbol *sym)
>  {
>         struct annotation *notes = symbol__annotation(sym);
>
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>         if (notes->src != NULL) {
>                 memset(notes->src->histograms, 0,
>                        notes->src->nr_histograms * notes->src->sizeof_sym_hist);
> @@ -864,7 +865,7 @@ void symbol__annotate_zero_histograms(struct symbol *sym)
>                         memset(notes->src->cycles_hist, 0,
>                                 symbol__size(sym) * sizeof(struct cyc_hist));
>         }
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>  }
>
>  static int __symbol__account_cycles(struct cyc_hist *ch,
> @@ -1121,7 +1122,7 @@ void annotation__compute_ipc(struct annotation *notes, size_t size)
>         notes->hit_insn = 0;
>         notes->cover_insn = 0;
>
> -       mutex_lock(&notes->lock);
> +       annotation__lock(notes);
>         for (offset = size - 1; offset >= 0; --offset) {
>                 struct cyc_hist *ch;
>
> @@ -1140,7 +1141,7 @@ void annotation__compute_ipc(struct annotation *notes, size_t size)
>                         notes->have_cycles = true;
>                 }
>         }
> -       mutex_unlock(&notes->lock);
> +       annotation__unlock(notes);
>  }
>
>  int addr_map_symbol__inc_samples(struct addr_map_symbol *ams, struct perf_sample *sample,
> @@ -1291,17 +1292,64 @@ int disasm_line__scnprintf(struct disasm_line *dl, char *bf, size_t size, bool r
>         return ins__scnprintf(&dl->ins, bf, size, &dl->ops, max_ins_name);
>  }
>
> -void annotation__init(struct annotation *notes)
> +void annotation__exit(struct annotation *notes)
>  {
> -       mutex_init(&notes->lock);
> +       annotated_source__delete(notes->src);
>  }
>
> -void annotation__exit(struct annotation *notes)
> +static struct sharded_mutex *sharded_mutex;
> +
> +static void annotation__init_sharded_mutex(void)
>  {
> -       annotated_source__delete(notes->src);
> -       mutex_destroy(&notes->lock);
> +       /* As many mutexes as there are CPUs. */
> +       sharded_mutex = sharded_mutex__new(cpu__max_present_cpu().cpu);
> +}
> +
> +static size_t annotation__hash(const struct annotation *notes)
> +{
> +       return (size_t)notes;
>  }
>
> +static struct mutex *annotation__get_mutex(const struct annotation *notes)
> +{
> +       static pthread_once_t once = PTHREAD_ONCE_INIT;
> +
> +       pthread_once(&once, annotation__init_sharded_mutex);
> +       if (!sharded_mutex)
> +               return NULL;
> +
> +       return sharded_mutex__get_mutex(sharded_mutex, annotation__hash(notes));
> +}
> +
> +void annotation__lock(struct annotation *notes)
> +       NO_THREAD_SAFETY_ANALYSIS
> +{
> +       struct mutex *mutex = annotation__get_mutex(notes);
> +
> +       if (mutex)
> +               mutex_lock(mutex);
> +}
> +
> +void annotation__unlock(struct annotation *notes)
> +       NO_THREAD_SAFETY_ANALYSIS
> +{
> +       struct mutex *mutex = annotation__get_mutex(notes);
> +
> +       if (mutex)
> +               mutex_unlock(mutex);
> +}
> +
> +bool annotation__trylock(struct annotation *notes)
> +{
> +       struct mutex *mutex = annotation__get_mutex(notes);
> +
> +       if (!mutex)
> +               return false;
> +
> +       return mutex_trylock(mutex);
> +}
> +
> +
>  static void annotation_line__add(struct annotation_line *al, struct list_head *head)
>  {
>         list_add_tail(&al->node, head);
> diff --git a/tools/perf/util/annotate.h b/tools/perf/util/annotate.h
> index 1c6335b8333a..962780559176 100644
> --- a/tools/perf/util/annotate.h
> +++ b/tools/perf/util/annotate.h
> @@ -271,8 +271,7 @@ struct annotated_source {
>         struct sym_hist    *histograms;
>  };
>
> -struct annotation {
> -       struct mutex lock;
> +struct LOCKABLE annotation {
>         u64                     max_coverage;
>         u64                     start;
>         u64                     hit_cycles;
> @@ -298,9 +297,15 @@ struct annotation {
>         struct annotated_source *src;
>  };
>
> -void annotation__init(struct annotation *notes);
> +static inline void annotation__init(struct annotation *notes __maybe_unused)
> +{
> +}
>  void annotation__exit(struct annotation *notes);
>
> +void annotation__lock(struct annotation *notes) EXCLUSIVE_LOCK_FUNCTION(*notes);
> +void annotation__unlock(struct annotation *notes) UNLOCK_FUNCTION(*notes);
> +bool annotation__trylock(struct annotation *notes) EXCLUSIVE_TRYLOCK_FUNCTION(true, *notes);
> +
>  static inline int annotation__cycles_width(struct annotation *notes)
>  {
>         if (notes->have_cycles && notes->options->show_minmax_cycle)
> --
> 2.41.0.162.gfafddb0af9-goog
>